4,282,035 8/1981 Nigrin /54 (viii) up to about 2% Lio, and

Transcription

1 USOO A United States Patent (19) 11 Patent Number: 5,985,473 Knapp (45) Date of Patent: Nov. 16, ) LOW-TEMPERATURE BARIUM/LEAD-FREE 5,292,690 3/1994 Kawachi et al.... 5O1/33 GLAZE FOR ALUMINA CERAMICS 5,362,687 11/1994 Tokunaga /21 5,518,968 5/1996 Knapp /14 75 Inventor: Randy Owen Knapp, Central, S.C. 5, /1997 Knapp /14 5,744,409 4/1998 Hashimoto et al /65 73) ASSignee: Cooper Automotive Products, Inc., 5,885,9 3/1999 Bako et al /66 Houston, TeX. FOREIGN PATENT DOCUMENTS 21 Appl. No.: 08/971, /1981 Japan. 22 Filed: Nov. 17, 1997 Primary Examiner Timothy Speer 6 Assistant Examiner Stephen Stein 51 Int. Cl.... B32B 9/00, CO3C 3/078 Attorney, Agent, or Firm Fish & Richardson, P.C. 52 U.S. Cl /702; 428/432; 427/427; 313/117; 501/14: 501/72 57 ABSTRACT 58 Field of Search /55, 65, 66, ---, /68, 69, 70, 72, 67, 14, 27, 26; 428/432, A barium lead-free ceramic glaze includes by weight: 701, 702; 313/118; 427/126.2, 397.7, 427 (i) between about 44 and 50% SiO, 56) References Cited (iii) between about 22 and 26% B.O.; U.S. PATENT DOCUMENTS (iv) between about 3 and 9% CaO; 2,972,543 2/1961 Beals /48 (v) between about 1 and 3% Sr0. 4,084,976 4/1978 Hinton /48 (vi) up to about 2% ZnO; 4,120,733 10/1978 Knapp /48 (vii) between about 2 and 4% KO; 4,256,497 3/1981 Knapp 106/ Y. 4,282,035 8/1981 Nigrin /54 (viii) up to about 2% Lio, and 4,316,963 2/1982 Hommel et al /14 (ix) between about 5 and 9% NaO. 4,547,625 10/1985 Tosaki et al /68.5 This barium/lead-free glaze can be effectually applied to a 4,624,934 11/1986 Kokubu et al /17 ceramic substrate at firing temperatures on the order of 50 4, /1988 Kondo et al /432 to 1650 F (843 to 899 C). 4,748,137 5/1988 Nigrin..., 501/46 4,814,298 3/1989 Nelson et al /17 5, /1993 Nigrin /21 17 Claims, No Drawings

2 1 LOW-TEMPERATURE BARIUM/LEAD-FREE GLAZE FOR ALUMINA CERAMICS BACKGROUND OF THE INVENTION The present invention relates to barium-free and lead-free ceramic glazes that can be employed with ceramic articles Such as Spark plug insulators. Glazes, continuous coatings that are fusion bonded onto a Substrate, can Serve a variety of purposes: (1) render the Substrate impermeable to liquids and gases; (2) aesthetics, e.g., covering blemishes and providing decorative effects, (3) protection; and (4) increased strength. One property of a glaze that can be particularly important is its thermal coefficient of expansion. In order to avoid undue stresses which can cause Spalling, chipping, cracking or crazing, a glaze should have a low thermal coefficient of expansion. A glaze preferably has a thermal coefficient that is Similar to the ceramic Substrate to which it is applied, e.g., on the order of from 6 to 7 microinches per inch per C. In fact, glazes having this low coefficient of thermal expansion can Strengthen an alumina insulator by inducing compres Sive Stresses at the Surface of the glaze-insulator composite. It is further recognized that glazes can be modified to change their properties, e.g., maturing temperature, color, and coefficient of thermal expansion. However, the highly complex, multi-component nature of glazes makes predict ing the effect of varying or Substituting chemical compounds in a glaze formulation difficult, even where the general properties of the individual components may be recognized. In addition, glazes are not homogeneous, that is, they may contain one or more dispersed undissolved phases, thus the ultimate components shown by chemical analysis may not effectively describe a glaze in a manner Such that the properties are readily predictable. The composition of glazes has evolved for other reasons. For example, lead found much use in traditional glazes, however, toxicity issues Surrounding lead have fostered the development of lead-free glazes. Examples of lead-free glazes can be found in U.S. Pat. No. 4, and U.S. Pat. No. 4,120,733. The composition described above includes 48 to 54% SiO, from 7 to 11%. Al-O, from 16.5 to 20% BO, from 11 to 14% BaO, from 2 to 3% CaO, from 2 to 2.5% ZnO, from 4.25 to 5.25% NaO, and from 0.4 to 1% KO, Li2O and MgO. Finally, glazes that are both lead-free and barium-free are also known. See, for example, U.S. Pat. No. 4,256,497. Spark plug insulators comprise one class of ceramic Substrates that are often used with a glaze. The exterior portions of Spark plug insulators are exposed to dirt and grease which may result in the formation of an electrically conducting Surface and premature failure of the Spark plugs. Because of this, alumina insulator bodies of Spark plugs are glazed to minimize dirt and grease build-up, and to increase the Strength and imperviousness of the Surface. However, the introduction of glaze onto Spark plugs has encountered its own Set of problems. For example, in the manufacture of a Spark plug, two separate firing Steps are typically employed in connection with an already Sintered bisque alumina insulator. The first involves glost firing raw-glazed insulators, i.e., the ceramic component of the plug, at F. ( C). A second firing step is then carried out at reduced temperatures, e.g., between 50 and 1650 F. (843 and 899 C), to incorporate a carbon-based, Fired-In Suppressor glass Seal that results in the production of Spark plug core assemblies, where a core assembly' is a glazed insulator with a contained internal center electrode component. Reduced temperatures are required in this Second firing Step due to the temperature-sensitive nature of certain of the components of the Fired-In Suppressor glass Seal. Moreover, the necessity for carrying out two Separate firing StepS adds to both the cost and the time involved in glazing and glass Sealing the unit. SUMMARY OF THE INVENTION The present invention relates to the Surprising discovery of barium-free and lead-free glazes that are capable of being fired at temperatures from F. below the tempera tures believed necessary to fire recognized compositions. In one aspect, the invention features a barium-free and lead-free ceramic glaze comprising, by weight: (i) between about 44 and 50% SiO, (iii) between about 22 and 26% B.O.; (iv) between about 3 and 9% CaO; (v) between about 1 and 3% SrO; (vi) up to about 2% ZnO; (vii) between about 2 and 4% K2O; (viii) up to about 2% LiO; and (ix) between about 5 and 9% NaO. In a Second aspect of this invention, a Spark plug includ ing an alumina insulator is coated with the above composi tion. The invention also relates to a method for applying a barium-free/lead-free glaze onto a ceramic article. This method includes (i) coating the ceramic article with a slurry firing the coated ceramic article at a temperature between 50 and 1650 F. (843 and 899 C). One area in which this method can be employed involves the manufacture of Spark plug assemblies. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS AS discussed above, the glaze according to the invention is barium-free, lead-free, and Substantially free of Zinc compounds. Moreover, this glaze is capable of being fired at a temperature of 1650 F. or less. By free it is meant that there is less than 0.25%, by weight of barium or lead compounds respectively in the glaze. By substantially-free is meant that there is less than about 2% by weight of Zinc containing compounds in the glaze. One example of a preferred ceramic glaze according to the invention comprises, by weight: (i) between about 44 and 50% SiO, (iii) between about 22 and 26% B.O.; (iv) between about 3 and 9% CaO; (v) between about 1 and 3% SrO; (vi) up to about 2% ZnO; (vii) between about 2 and 4% KO; (viii) up to about 2% LiO; and (ix) between about 5 and 9% Na2O, with the balance being minor impurities.

3 3 4 More preferred glazes have the following composition: tics. Because of this, glaze ceramists commonly use a System of expressing oxide compositions in terms of molar TABLE I proportions, i.e., molecular equivalents. By means of molecular equivalents, an empirical oxide formula can be OXDE PERCENT BY WEIGHT 5 calculated for each glaze composition. SiO, For purposes of arriving at an empirical molecular Al2O BO formula, oxides are classified as either basic, neutral (or CaO amphoteric), or acid. The glaze oxides which are classified SrO as bases, that is, the alkali metal and alkaline earth oxides,. are designated as RO and RO respectively. The neutral io os-1s or amphoteric oxides are designated as "RO while acid NaO oxides are designated as "RO. The empirical molecular formula basis of the glaze com - f E 1 d 1b that in thi In looking at the individual oxides present in the glazes, position or examples 1a an al appear later In LnIS one should keep in mind the following: specification, is shown in Table II below: TABLE II MOLES NORMALIZED WEIGHT MOLECULAR (Wt./Molecular MOLE OXDE SYMBOL % WEIGHT Wt.) FRACTION SiO, RO, O Al2O RO O.O990 O.33O B.O. RO 24O O CaO RO O.O778 O.260 SrO RO 2.OO O.O193 O.064 ZnO RO O.O2 O.O51 KO RO O.O319 O.106 LiO RO O.148 NaO RO O O.1111 O.371 Impurities Trace N/A N/A N/A Control of the amount of Silica is important, Since if the 35 Silica is too high, the glaze normally becomes excessively refractory; if the silica is too low, the glaze in many cases, depending on other ingredients present, can become too Soluble and, therefore, unstable. T In establishing the empirical formula for a glaze, the formula is normalized so that the sum of RO and RO is brought to unity. For example, in Table II, the sum of RO plus RO equals mole; dividing each of the MOLES obtained by the total moles of RO and RO establishes the NER, al that A. other spent E. " empirical formula for the glaze, given in the last column as greatly modify the effect of the silica present. For example, alumina can increase the Viscosity and retard macrocrystal line growth. High Viscosity is typically undesirable in a Normalized Mole Fraction. By means of the empirical formula, the calculation of batch weights or the determina tion of the proportions of ingredients required to produce a glaze because it prevents healing of pinholes, Scratches, and - 0 X other minor flaws. 45 glaze having a given formula is simplified, especially if it is The alkalies are strong fluxes and can increase the fluidity of the molten glaze. Increasing the amount of alkali com- pounds present in the glaze can increase the coefficient of thermal expansion, and can have a direct bearing upon crazing of the glaze. The alkaline earths can also act as Vigorous fluxes in a glaze composition. For example, CaO can act as a flux at d d temperatures of 2,000 F. (1093 C.) and above; excess desired to formulate the glaze from compounds other than oxides, Such as for example, carbonates. Further, the CO parison of glaze formulations can be greatly simplified. In the context of the invention, both suitable and preferred so arrays are set forth in Table III. TABLE III MOLECULAR calcia can cause loss of refractoriness and devitrification, EOUIVALENTS leading to a low-gloss matte texture, possibly as the result of 55 OFOXIDE COMPONENT formation of anorthite (CaO.SiO). Magnesia can act as a Vigorous flux at higher temperatures, and can lower the Oxide Symbol Suitable Preferred coefficient of thermal expansion to a far greater degree than SiO, RO, other bases. Al2O RO O The ultimate composition of a glaze, particularly a glaze 60 BO RO O id b lex. AS discussed CaO RO containing ten or more oxides, can be complex. SrO RO O.O above, this complexity can make predicting the effect of ZnO RO O.O O.O varying or Substituting chemical compounds in a glaze KO RO O.O formulation difficult. However, the raw materials of glazes LiO RO O.O7-O.22 O NaO RO O are typically oxides or compounds that can be expressed as 65 oxides, thus enabling the components to be described in terms of phase' compositions having known characteris

4 S The barium and lead-free ceramic glazes of the present invention can be applied to any of these ceramic Substrates, e.g., high alumina ceramic Substrates, which are typically coated with a glaze. Included among Such Substrates are chemical laboratory ware, washers, Spacers, tubes, electrical circuit components, power delivery insulators, Sound isola tion tiles, etc. One particularly preferred Substrate is a Spark plug insulator, which itself is typically made of 85 to 95% by weight alumina. The glaze can be formulated into a water-based slip or Slurry in accordance with techniques well known in the art. For example, the slip can be prepared by combining the glaze composition, often in a pre-melted or fritted form, with water and other optional minor ingredients to form a slip having a Solids content ranging between about 40 and 60%. These optional components include naturally occurring raw materials, Such as feldspar, limestone and clays. Other Suitable additives include organic binder(s) Such as emulsi fied wax, starches including (STARAMICR), polyvinyl alcohol (PVA) and methylcellulose. After formation, the Slip is applied to the ceramic Sub Strate by well-recognized means Such as roller flooding, dipping or Spraying. The coated article then is fired. Such firing can be carried out at a temperature well below that traditionally employed in the art. For example, where the glaze is sprayed onto the substrate, a firing temperature can be 1650 F. or below, preferably between 50 and 1650 F. (843 and 899 C.), can be used. On the other hand, a temperature less than about 1800 F., preferably between 1700 and 1800 F (927 and 982 C.), can be employed for roll-on and dipped applica tions. While the exact manner of firing is not critical to the present invention, firing typically is carried out in a Suitable device, e.g., a glost kiln, for a period between 10 and 90 minutes. The firing cycle and its duration are designed to render a Smooth, uniform glaze coating of high gloss and good Strength. The invention is capable of producing a number of Significant advantages over the prior art. AS mentioned above, the low temperature barium-free/lead-free ceramic glaze of the present invention can be fired at a temperature which is 250 to 400 F (121 to 204 C) below that of 45 traditional lead-free ceramic glazes. Moreover, the proper 40 6 typically 40-60% above that of bisque ware without glaze. In addition, the invention can provide Smoother coatings having higher gloss and fewer included bubbles, pinholes, etc. It also allows for more brilliant underglaze decorations. The following examples are given by way of illustration and in no way should be construed as limiting the present invention. EXAMPLES Examples 1a and 1b Bisque-fired Spark plug insulators including 90% alumina were coated, by means of (a) spraying with a glaze Slip composition including 55% by weight of solids and (b) rolling on a glaze Slip composition including 45% by weight Solids and comprising: OXIDE TABLE IV PERCENT BY WEIGHT SiO, 46.9 Al-O BO CaO 4.4 SrO 2.O ZnO 1.2 KO LiO O NaO TiO, Fe-O, MgO 6.9 O.2 *Formulae reported herein represent fired compositions, disregarding volatization, if any, of Oxide ingredients during firing. In Example 1a, the Spray-coated ceramic was then fired at F (885 C.) for minutes to form a smooth, uniform glaze of high gloss and good strength. There was no evi dence of crazing or devitrification in the glaze and there was achieved a strength increase of about 46% over bisque. In Example 1b, the ceramic coated by rolling on was fired at 1775 F (968 C.) for 30 minutes and gave a 52% increase over bisque. Examples 2-17 The above procedure was repeated with similar results for glazes of the following compositions: OXDE TABLE 4 SiO, Al2O O B.O CaO SrO ZnO O.8 O.9 O.8 1.O 1.2 KO LiO O.8 1.O O NaO 9.O O 7.O 7.4 Minor O.1 O.1 O2 O2 O2 Impurities O O O O O O1 O.2 O.1 O.2 O.2 O.1 O1 O1 O2 O1 O1 ties of the glazed product are the same or better than that 65 associated with more traditional glazes. For example, the breaking Strength of insulators with the invention glaze is Tables VI-VIII illustrate the normalized mole fractions for Example 1-17.

5 7 TABLE VI 8 TABLE VIII-continued EXAMPLES I-VI Oxide Symbol I II III IV V VI SiO, RO, Al-O. RO O O.426 O.3OO O.314 O.364 BO RO :210 CaO RO O.26O O.199 O.195 O.397 O.331 O.204 SrO RO O.O64 O.O44 O.O51 O.O39 O.O49 O.O67 ZnO RO O.O51 O.O34 O.O39 O.O3O O.O39 O.051 KO RO O O.124 O.1O2 O.1O2 O.114 LiO RO NaO RO O.371 OSOf O.473 O.349 O.361 O.413 Minor N/A N/A N/A N/A N/A N/A N/A Impuritives TiO2, Fe2O3, MgO * Sum of RO and RO Groups equals 1.00 ( unity). TABLE VII EXAMPLES VI-XII Oxide Symbol VII VIII IX X XI XII SiO, RO, Al2O RO O O.318 O.249 O.290 O.223 BO RO O.973 CaO RO O.217 O.359 O O.293 O.443 SrO RO O.O72 OO61 O.O75 O.O59 O.O73 O.057 ZnO RO KO RO O.108 O.O97 O.104 O.091 O.101 O.O85 LiO RO O.169 O O NaO RO O.376 O.3OO O.343 O.267 O.307 O.243 Minor N/A N/A N/A N/A N/A N/A N/A Impuritives TiO2, Fe2O3, MgO * Sum of RO and RO Groups equals 1.00 ( unity). TABLE VIII EXAMPLES XIII-XVII Oxide Symbol XIII XIV XV XVI XVII SiO, RO, Al2O RO O.299 O.259 O.271 O.275 O.246 BO RO , CaO RO O.251 O.336 O.307 O.271 O.311 SrO RO O.081 O.O76 O.O78 O.086 O.O8O ZnO RO O O.O60 OO69 O.O66 KO RO O.O99 O.093 O.O93 O.O98 O.O9. LiO RO O.190 O O.199 O EXAMPLES XIII-XVII Oxide Symbol XIII XIV XV XVI XVII NaO RO O.313 O.269 O.277 O.277 O.261 Minor N/A N/A N/A N/A NAA N/A Impuritives TiO, Fe2O, MgO *Sum of RO and RO Groups equals 1.00 ( unity). In the above examples, the Spray coated ceramic Substrate was fired at a temperature of 1625 F (885 C) for minutes. Although certain preferred embodiments of the invention are specifically illustrated and described above, it will be appreciated that various modifications, variations, Substitutions, omissions, changes and the like to the present invention can be made in light of the above teachings and Such are within the purview of the appended claims without otherwise departing from the Spirit and intended Scope of the invention. What is claimed is: 1. A barium/lead-free ceramic glaze comprising, by weight: (i) between about 44 and 50% SiO, (iii) between about 22 and 26% B.O.; (iv) between about 3 to 9% CaO; (v) between about 1 and 3% SrO; (vi) up to about 2% ZnO; (vii) between about 2 to 4% KO; (viii) up to about 2% LiO; and (ix) between about 5 and 9% NaO. 2. The lead-free ceramic glaze of claim 1 comprising, by weight: (i) between about 44.1 and 49.8% SiO, (ii) between about 7.7 and 12.3% Al-O; (iii) between about 22.9 and 25.1% B.O.; (iv) between about 3.1 and 8.5% CaO; (v) between about 1.3 and 2.7% SrO; (vi) between about 0.8 and 1.7% ZnO; (vii) between about 2.7 and 3.3% KO; (viii) between about 0.8 and 1.8% LiO; and (ix) between about 5.1 and 9.0% NaO. 3. The lead-free ceramic glaze of claim 1 comprising, by weight: (i) about 47% SiO2; (ii) about 10%. Al-O; (iii) about 24% B.O.; (iv) about 4.5% CaO; (v) about 2.0% SrO; (vi) about 1.2% ZnO; (vii) about 3.0% KO; (viii) about 1.3% LiO; and (ix) about 7.0% NaO.

6 4. A ceramic Substrate coated with the composition of claim The ceramic Substrate of claim 4 wherein said Substrate is an alumina insulator of a Spark plug. 6. A ceramic Substrate coated with the composition of claim The ceramic Substrate of claim 6 wherein said Substrate is an alumina insulator of a Spark plug. 8. A ceramic Substrate coated with the composition of claim The ceramic Substrate of claim 8 wherein said Substrate is an alumina insulator of a Spark plug. 10. A method for applying a barium/lead-free glaze to a ceramic comprising the steps of (i) Spraying said ceramic with a slurry including the composition of claim 1 and firing Said coated ceramic at a temperature not greater than 1650 F. 11. The method according to claim 10, where the firing temperature is between 50 and 1650 F. 12. A method for applying a barium/lead-free glaze to a ceramic comprising the steps of (i) Spraying said ceramic with a slurry including the composition of claim 2 and 5 10 firing Said coated ceramic at a temperature not greater than about 1650 F. 13. The method according to claim 12, where the firing temperature is between 50 and 1650 F. 14. A method for applying a barium/lead-free glaze to a ceramic comprising the steps of (i) Spraying said ceramic with a slurry including the composition of claim 3 and firing Said coated ceramic at a temperature not greater than about 1650 F.. The method according to claim 14, where the firing temperature is between 50 and 1650 F. 16. A method for making a Spark plug core assembly including an alumina insulator component and a Fired-in Suppressor glass Seal component comprising: (i) Spraying the alumina insulator component with a slurry comprising the composition of claim 1, and (ii) Simultaneously firing both the alumina insulator component and the Suppressor glass Seal component to form a glazed and glass Sealed core assembly, Said firing being carried out at a temperature not greater than about 1650 F. 17. The method according to claim 16, where the firing temperature is between 50 and 1650 F. k k k k k